Feed: update: Added a summary at the end

Hello tontof!

Here is a very small change just to add a summary at the end of the update:

> A new row has been added to show the number of items, the number of errors/succeses/up-to-date and the total elapsed time.
> Note: the time column now displays the elapsed time to update each corresponding item and not the elapsed time since the first action.

I don't know if you want it but I wanted to have this summary and this is why I added it

Note that I'm not so familiar with PHP and I hope that I've respected your conventions :-)
Feel free to modify the code or to reject the pull request if you don't like it ;-)

Also, I didn't installed php5 just to update the locale files, this is why `$messages['fr_FR']` variable has not been updated in 'index.php' file (I just updated `locale/fr_FR/LC_MESSAGES/messages.po` by hand) :-)